Place the pecans in a medium skillet over medium-high heat. Toast them without oil, stirring frequently, until they begin to brown lightly and emit a nutty aroma. Remove from heat and let cool completely before chopping coarsely.

Line a 9 x 13-inch baking pan with aluminum foil, ensuring it covers the bottom and sides completely. Sprinkle half of the chopped pecans evenly across the base of the pan. Reserve the remaining pecans for the topping.

In a large, heavy-bottomed saucepan, combine the butter, sugar, corn syrup, and salt. Attach a candy thermometer to the side of the pan, ensuring the tip is submerged in the mixture but does not touch the bottom.

Place the pan over medium heat and cook, stirring constantly, until the butter has melted. Continue cooking, stirring occasionally, until the sugar dissolves and the mixture becomes golden brown.

Allow the temperature to reach between 295°F and 305°F (hard crack stage). This process typically takes 10 to 15 minutes.

Carefully pour the hot toffee mixture over the pecans in the prepared pan. Spread evenly with a heatproof spatula. Tap the pan gently on the counter to release any trapped air bubbles.

Allow the toffee to cool for 2–3 minutes. Sprinkle the chopped chocolate evenly over the warm toffee. Let it sit for another 2–3 minutes until the chocolate begins to soften, then spread it smoothly with an offset spatula or the back of a spoon.

Sprinkle the remaining chopped pecans over the melted chocolate. Press lightly to ensure they adhere to the surface.

Let the toffee cool completely at room temperature for approximately 1 hour. Once cooled, refrigerate for at least another hour or overnight until firm.

Once the toffee is fully set, lift it from the pan using the foil. Peel the foil from the bottom and break the toffee into irregular pieces using your hands or a sharp knife.

Store the toffee in an airtight container in the refrigerator for up to 3 months, layering parchment paper between pieces to prevent sticking.